泌尿道感染（urinary tract infection，UTI），也称为急性膀胱炎或膀胱感染，是一种会影响到部分泌尿道的感染。泌尿道分为上、下泌尿道，感染部位不同对应到不同疾病名称：当影响到下泌尿道，称为膀胱炎；当影响到上泌尿道，也就是肾脏的时候，则称为肾盂肾炎。

不同感染位置，症状会稍有不同：下泌尿道感染的症状主要是解尿时会疼痛，也可能会有频尿或是一直想要解尿的感觉；上泌尿道感染除了会有跟下泌尿道感染同样症状外，还会有发烧、腹痛的症状。有些情况，可能没有解尿也能感受到尿道灼热痛感。年长者和很年轻的人若感染，以上症状可能不会表现得十分明显。最常见造成泌尿道感染（上下泌尿道都有可能）的病菌是大肠杆菌，而其他细菌、病毒或霉菌则鲜少造成感染。

A urinary tract infection (UTI) is an infection that affects part of the urinary tract. When it affects the lower urinary tract it is known as a bladder infection (cystitis) and when it affects the upper urinary tract it is known as kidney infection (pyelonephritis). Symptoms from a lower urinary tract include pain with urination, frequent urination, and feeling the need to urinate despite having an empty bladder. Symptoms of a kidney infection include fever and flank pain usually in addition to the symptoms of a lower UTI. Rarely the urine may appear bloody. In the very old and the very young, symptoms may be vague or non-specific.